It is known that color images may be obtained from imagewise exposed silver halide photographic elements by development with a primary aromatic amine color developing agent in the presence of a color coupler. The oxidized color developing agent formed in the areas of silver halide development couples with the coupler to form a dye. The coupler is normally incorporated in the sensitive photographic element.
It is also known that 5-pyrazolones in which the 4-position of the pyrazolone ring is free, that is having only hydrogen substituents (4-equivalent magenta couplers), can be used as magenta couplers in color photographic elements to provide magenta dye images having useful properties. Examples of such couplers are the 4-equivalents 3-anilino-5-pyrazolone couplers described in, for example, U.S. Pat. Nos. 3,519,429, 3,907,571, 3,928,044, 3,935,015 and 4,199,361. However, 4-equivalent 5-pyrazolone couplers have a number of disadvantages, as they require four equivalents of silver to produce each molecule of dye, are sensitive to certain chemical vapors, for example formaldehyde, and have poor dye light and dye dark stability. These drawbacks can be overcome by using so-called 2-equivalent 5-pyrazolone magenta couplers in which a substituent is introduced into the coupling position (4-position) of the coupler and eliminated as a leaving group (coupling-off group or splitting-off groups) during the color development process, thus requiring only two equivalent of silver in order to produce each molecule of dye.
Among coupling-off groups known in this connection are the arylthio groups described, for example, in U.S. Pat. Nos. 3,227,554, 3,701,783, 3,935,015, 4,351,897, 4,413,054, 4,556,630, 4,584,266, 4,740,438, 4,853,319, 4,876,182, 4,900,657, 4,929,540, 4,942,116, 5,250,407, 5,262,292, and 5,256,528; WO 88/04795, 92/18902, and 93/02393; EP 341,204, and GB 1,494,777.
2-equivalent 1-aryl-3-anilino-4-phenylthio-5-pyrazolone magenta couplers have been described, for example, in U.S. Pat. Nos. 4,413,054; 4,556,630; 4,584,266; 4,900,657; U.S. Pat. No. 5,256,528 and in GB 1,494,777 and in WO Patent Application 92/18902.
U.S. Pat. No. 5,663,040, discloses a silver halide photographic element comprising a support and at least one silver halide emulsion layer having a 2-equivalent 1-phenyl-3-anilino-4-phenylthio-5-pyrazolone magenta coupler, wherein both the 3-anilino and 4-phenylthio groups comprise a ballasting group, the 4-phenylthio group comprises a carbamoyl group being in 2-position with respect to the carbon atom attached to the sulfur atom and bearing said ballasting group, and the sum of sigma values of substituents on the 1-phenyl and the 3-anilino groups is less than 1.3.
In the subtractive color photography, blue sensitive, green sensitive and red sensitive layers are so constructed that yellow, magenta and cyan color images are formed, respectively. However, each of the dyes formed as color images has not always ideal absorption characteristics. For instance, the magenta dye image not only has a necessary green color absorption but also generally absorbs a blue color more or less, with the result that distortion is brought about in respect of color reproduction. In order to remove such distortion of color reproduction there are generally employed so called colored magenta couplers which exhibits a yellow color when they do not cause the coupling reaction as magenta couplers.
As such colored magenta couplers there have been known 4-arylazo-5-pyrazolones having at the 1- or 3-position a substituent containing a long-chain hydrocarbon group imparting a diffusion resistance to the couplers, such as disclosed in the specifications of U.S. Pat. Nos. 2,428,054; 2,449,966 and 2,455,170, 1-phenyl-4-arylazo-5-pyrazolones having at the 3-position a 2-halogeno-5-alkylamino-anilino or 2-halogeno-5-acylamino-anilino group, such as disclosed in Japanese Patent Publication No.15754/69, and the like.
However, 5-pyrazolones having an arylazo substituent at the 4-position have generally a lower rate of coupling with an oxidation product of a p-phenylene diamine derivative than 5-pyrazolones having no substituent at the 4-position, and therefore, in the case of 4-arylazo-5-pyrazolones it is difficult to obtain a sufficient photographic sensitivity and a sufficient dye density.
5-Pyrazolones having an anilino group at the 3-position have a very high coupling rate, and they are characterized in that their coupling rate, even in the case of 3-anilino-5-pyrazolones having an arylazo group introduced in the 4-position, is much higher than that of other 5-pyrazolones.
U.S. Pat. No. 4,070,191 discloses a 4-arylazo-5-pyrazolones colored magenta coupler which has a high coupling rate and gives a masked dye image having an absorption maximum wavelength in the blue ray region ranging from about 430 to about 460 m.mu.
U.S. Pat. No. 4,163,670 discloses a color photographic material containing a 5-pyrazolone derivative forming magenta dyestuff, in conjunction with red- and blue-sensitive emulsions containing phenol or a-naphthol and an open-chain ketomethylene compound forming blue and yellow dyestuffs respectively. The 5-pyrazolone magenta derivative has excellent spectral absorption characteristics and fastness and can be used in high temperature processing without fogging and desensitisation.
U.S. Pat. No. 5,853,971 discloses a color photographic material containing on a support at least one red-sensitive, green-sensitive and blue-sensitive silver halide emulsion layer together with interlayers between layers of different colour sensitivity, wherein at least one of the stated interlayers contains a masking coupler, the masking coupler having a defined reaction rate constant for the coupling reaction with the developer oxidation product, obtaining an improved sensitivity without increase of granularity.
U.S. Pat. No. 5,667,946 descibes a photographic silver halide emulsion layer having associated therewith a 1-(4-chlorophenyl)-3-(monosubstituted amino)-5-pyrazolone magenta coupler. Masked magenta coupler known in the art can be used in combination with such magenta couplers to give an improved spectral absorption curve.
U.S. Pat. No. 5,466,568 discloses a photographic element containing an azopyrazolone masking coupler and a ballasted aromatic nitro compound having a reduction peak potential which is more positive than -1.3 V vs. the Standard Calomel Electrode to exhibit reduced fog.
A problem of the photographic materials described in the art is the low speed and contrast obtained by the use of the magenta couplers and the colored magenta couplers used therein. An object of the present invention is to solve this problem, without a detrimental effect on the other sensitometric properties, such as Dmin and Dmax.